Muwatta Malik 634
موطأ مالك#634SahihYahya related to me from Malik from Nafi that Abdullah ibn Umar used to say, "Only some one who makes the intention to fast before dawn (actually) fasts
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliMauquf Sahih
In-book reference: 18:5